I think that you are just being difficult again Hyp 
But I'll certainly try to support my 'assertions'.
From the SRD (only resource available to me at this moment), under Tactical Movement:
Another quote exists in the PHB (can't find it in the 3.5 SRD that creatures wielding reach weapons (and creatures with reach) threaten 2 squares all around them (including the 2 diagonals, which is listed as an exception to the rule about 2 diagonals being 15ft).
Once again from the SRD, this time under Cover:
And again from the SRD, this time under Concealment:
These last 2 quotes clearly relate to those specific conditions under combat modifiers. In no way are they used for calculating distance between squares. Otherwise, you could 'hide' in a corner of your square and be out of 'reach' from the medium-sized opponent in the adjacent square, thereby negating AOOs.
Distance is measured from centre of squares. Using the corners is only a mechanism for determing cover and concealment.

But I'll certainly try to support my 'assertions'.
From the SRD (only resource available to me at this moment), under Tactical Movement:
Measuring Distance
Diagonals: When measuring distance, the first diagonal counts as 1 square, the second counts as 2 squares, the third counts as 1, the fourth as 2, and so on.
Another quote exists in the PHB (can't find it in the 3.5 SRD that creatures wielding reach weapons (and creatures with reach) threaten 2 squares all around them (including the 2 diagonals, which is listed as an exception to the rule about 2 diagonals being 15ft).
Once again from the SRD, this time under Cover:
To determine whether your target has cover from your ranged attack, choose a corner of your square....
And again from the SRD, this time under Concealment:
To determine whether your target has concealment from your ranged attack, choose a corner of your square.......
These last 2 quotes clearly relate to those specific conditions under combat modifiers. In no way are they used for calculating distance between squares. Otherwise, you could 'hide' in a corner of your square and be out of 'reach' from the medium-sized opponent in the adjacent square, thereby negating AOOs.
Distance is measured from centre of squares. Using the corners is only a mechanism for determing cover and concealment.